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Binoculars review

Pentax SD 9x42 WP

The S series of Petnax binoculars consists of a wide array of models. You can find among them porro prismatic, waterproof SP WP devices, SP instruments devoid of any waterproof qualities, and also three roof prism models marked as SD WP.

The roof prism binoculars feature Schmidt-Pechan prism system. Apart from classic SD 8×42 WP and SD 10×42 WP parameters Pentax of course had to add something less typical - we mean here the SD 9×42 WP model. As WP letters in its name indicate, you deal with binoculars fully submersible up to a depth of 1 meter.

The 8×42 and 10×42 models feature classic casings but the SD 9×42 WP is an open hinge design. Still all these constitute an interesting choice for buyers which look for a pair of binoculars with a good price-quality ratio.

In the case of the tested device Pentax boast of applying three types of coatings: high quality multilayer antirelection coatings on all air-to-glass surfaces, special reflective coatings on the prisms, and also hydrophobic coatings on outer elements.

Buyers get in the box: caps for objective lenses and eyepieces, a strap and a case. The product comes with a 30-year warranty period of the producer.

Visible in the centre but without any serious problems. Distinct on the edge.

4.4/10.0

Astigmatism

Moderate.

7.2/10.0

Distortion

Distance between the first curved line and the field centre compared to the field of view radius : 98% +\- 2%

10/10.0

Coma

Appears far from the centre, in a distance of 75% of the field of view radius and is medium on the edge.

8.1/10.0

Blurring at the edge of the FOV

Blur occurs in a distance of 78% ± 3% from the field of view centre.

5/10.0

Darkening at the edge the FOV

Negligible.

4.8/5.0

Whiteness of the image

Untypical transmission graph with the highest values for blue part of the spectrum. Small wonder the image is distinctly bluish.

1.8/5.0

Collimation

Perfect.

5/5.0

Internal reflections

Left:

Right:

Dark areas around pupils.

4/5.0

Housing

Small and very handy for the 42 mm class and the open hinge design. Good quality rubber armour which sticks to your hands well but is a bit loose near the objective lenses. Indentations for thumbs. Rubberized eyecups with 4 detention stops. Produced in China.

7.5/8.0

Focusing

Huge, comfortable and ribbed central wheel which moves smoothly and is well damped. Running through the whole distance scale takes a turn through an angle of 550 degrees. A ring on the right eyepiece moves the outer element and is a bit too hard to move.

4.3/5.0

Tripod

At the front of the instrument, far from the gravity centre.

2/3.0

Interpupilary distance

from 56 to 73.5mm

4/6.0

Closest focusing distance

1.7 meters.

2/2.0

Eyepieces FOV

Apparent field of view of 54.3 degrees.

5.5/10.0

Field of view

Measured by us amounted to 6.07 ± 0.04 degrees and it in accordance with official specifications. A typical field for this class of equipment.

The transmission graph was one of the most interesting and untypical thing we noticed during the test of the Pentax SD 9x42 WP. We present it below.

It is clear the coatings are optimized for blue light; at that point the transmission reaches 85%. Unfortunately in the centre of the visible spectrum the transmission level is just 78% and for red light it drops even further, to a level less than 75%. As a result, images from this instrument can hardly be called bright but they certainly deserve to be called blue. It’s hard to guess the Pentax optics specialists’ reasons behind choosing these coatings and not any other. Fans of nighttime observations might suggest that our retinal rods are more sensitive to blue light than cones which are active during the day. If it was the guideline then the specialists went a bit over the top. The rods reach the maximum of their sensitivity near 505 nm and the maximum transmission of the SD 9x42 WP amounts to 450 nm, so a point where the efficiency of rods decreases to about 60% of its maximum performance.

Apart from that very specific transmission graph too high chromatic aberration is the only flaw of the tested Pentax; in other categories the binoculars fared decently well, good or even very good. The instrument didn’t have any problems with distortion, coma, astigmatism or brightness loss on edges of the field of view. What’s more, the optics is hidden inside a very robust, waterproof casing; you also get good quality prisms and 30 years of warranty period. The quality control also performed very well – the build, darkening and cleanliness inside the tubes is beyond reproach.

If not for these unfortunate coatings we would get a really interesting, well-done device with original parameters and a pretty sensible price tag too. Even with that slip-up, though, the Pentax SD 9X42 WP managed to accumulate as many as almost 127 points in our test, placing it on a really good level. Better transmission results and colour rendering would mean a result exceeding 130 points and a very high overall assessment. Pity.

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